Tube key



FIG. 1 is a perspective view of a tube key showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a left end plan view thereof; and,

FIG. 7 is a right end plan view thereof. 

The ornamental design for a tube key, as shown and described. 